1. Field of the Invention
This invention relates to transferring electric power generated by multiple sources of AC power to a utility grid without first rectifying and thereby first transferring the electric power of all AC inputs into a common two wire DC bus.
2. Detailed Background of the Invention
Two patents, U.S. Pat. Nos. 8,049,351 and 8,178,987, for horizontal axis windmill designs, by Mahawili describe an electrical generating structure with two major components that are shown in FIG. 9. First, there are rotating permanent magnets attached to the periphery of a windmill rotor and second there is a stator constructed from a multiplicity of coil pairs, which are located in a stationary ring structure surrounding the periphery of the rotor of the windmill. (The word “stationary” means stationary with respect to the rotor, the windmill itself still turns around its vertical axis for the purpose of facing into the wind.)
As shown in a cross-sectional view in FIG. 10, a pair of coils 97 in the stator form a U-shaped channel within which the permanent magnets 98 move. When viewing FIG. 10 the reader should assume that the movement of the magnet is perpendicular to the plane of the paper, i.e. the movement of the magnet is either into or out of the paper. The movement of these magnets generate voltages in the coil pairs by Faraday's law, which thus convert the mechanical energy of the windmill into electrical energy.
This windmill design has been implemented by the firm Windtronics and the design consists of 6 permanent magnets rotating within a U-shaped channel of 68 coil pairs. The fact that the number of permanent magnets is much smaller than the number of coil pairs in the stator leads to an unusual property. As a permanent magnet flies by a coil pair, that coil pair generates one complete AC voltage wave (or cycle) consisting of one positive half wave and one negative half wave. Another AC voltage wave is not generated in a particular coil pair until the next permanent magnet flies by. So each coil pair generates an AC voltage wave only some of the time, but looking at all coil pairs together, there are always some coil pairs that are generating AC voltage waves at any moment in time. Also, the fact that the number of stator coil pairs is not divisible by 3, leads to the property that the voltage waves generated by one permanent magnet pair has a three phase relationship with the voltage waves generated by the other two permanent magnet pairs. It should be mentioned that the six permanent magnets are equally distributed around the periphery of the rotor as shown in FIG. 9; therefore, the angular distance between adjacent magnets is 60 degrees. A permanent magnet pair is defined as two magnets that are located at opposite sides of the periphery.
For the current implementation by Windtronics, in order for the electric power generated by this windmill to be transferred to the utility grid, the AC voltage waves generated by each of the 68 coil pairs are rectified into DC by 68 separate full wave rectifiers consisting of 4 diodes each physically located next to each coil pair. The DC output of each of these full wave rectifiers is connected to a two wire DC bus also located around the periphery, which is connected through slip rings and cabling to a conventional commercially available DC to AC inverter for connection to the utility grid, which is typically located in a building located near the windmill.
It is the object of this invention to improve on the circuits that transfer the AC power generated by the windmill, such that the rectifying step, which currently transfers all AC power through full wave rectifiers to a common DC bus, is eliminated and all input AC half waves are separately and directly injected into the utility grid. The elimination of the rectifying step into a common DC bus increases the efficiency of the conversion process by eliminating some of the diodes that would otherwise be used and therefore eliminates the losses that these diodes would incur. It is an additional object of this invention to make this converter small enough, so that all the required components fit into the windmill itself, such that the windmill can be connected directly to the utility grid; which is a desirable feature, because all the work and expense of providing a separate inverter will be eliminated.
3. Description of the Prior Art
U.S. Pat. No. 6,122,182 by Mihail Moisin describes an AC to AC scheme for powering gas discharge lamps. The cited patents: U.S. Pat. No. 4,468,725 by Colin Schauder, U.S. Pat. No. 4,896,091 by Andre Kislovski, U.S. Pat. No. 5,005,115 by Colin Schauder and U.S. Pat. No. 5,010,471 by J. Ben Klaassens et. al. are AC to AC converter systems of various kinds; but none of them deal with the task of injecting variable frequency alternating current pulses from a multiplicity of sources into the constant frequency utility grid.
This invention is also related to U.S. Pat. No. 5,892,664 by this inventor (Dietrich Vedder), which also deals with the task of transferring variable frequency AC power into a utility grid, but uses complete rectification of the input AC power.